Regarding an inverter drive device for driving a motor by controlling PWM (pulse-width modulation), an asynchronous PWM method that controls PWM by making carrier frequency constant with respect to variable output frequency of an inverter is widely used. Accordingly, when the inverter output frequency becomes high, the number of PWM pulses reduces and output errors of the inverter increase. Further, output voltage errors increase in an overmodulation mode in which the inverter output voltage command is more than the maximum output level of the inverter (sinusoidal wave). Especially, the imbalanced state of positive side voltage integration (positive voltage) and negative side voltage integration (negative voltage) which are switched in a half cycle of AC output makes the motor control unstable. Thus, it is desired to adjust to make the positive voltage and the negative voltage of the inverter output become roughly equal by adjusting modulated wave near the zero crossing of the output voltage.
PTL 1 describes a technique to minimize output voltage error by setting a 50% duty cycle near the zero crossing of the inverter output voltage.
Further, PTL 2 describes a technique to drive the inverter within a range of a modulation factor that does not cause an inverter output error.
Further, PTL 3 describes a technique to change carrier frequency according to inverter output frequency so that the inverter output error becomes small.